1. Field of the Invention
The invention relates to a refractory ceramic mass as well as to its use.
2. Description of the Background Art
Specifically the invention relates to a basic refractory ceramic mass based on MgO sinter (sintered magnesia). MgO sinter is an essential component of all MgO and MgO-spinel-products. In mineralogy MgO sinter is called periclase. A main raw material for the production of MgO sinter is magnesite, i.e. magnesium carbonate or a synthetic magnesia basis respectively. To adapt specific material behaviours, specifically in order to improve the chemical resistance against slags, to improve ductility as well as temperature change resistance refractory ceramic masses based on MgO sinter in combination with various additional components are known. This includes chromite (chromic ore) for the production of so called magnesia chromite bricks. The advantages of such bricks are less brittleness and higher ductility respectively compared with pure magnesia bricks. Furthermore a better corrosion resistance against non basic slags is presented.
Although such products have been proofed in the past there is a permanent object to optimize refractory ceramic masses and workpieces (moulds) made thereof. For example products are required for the lining of industrial furnaces, wherein considerable mechanical forces onto said refractory lining may be expected, which brittleness being as small as possible. This Includes for example rotary kilns in cement industry where considerable mechanical forces onto the refractory lining may be expected because of a deformation of the furnace but as well furnaces in the steel- and non-ferrous metal industry, where mainly thermal stresses lead to problems during heat up and temperature changes.
If chromite containing products are used a relatively high content of alkalis and carburizing conditions, mainly based on the fuel used in an industrial furnace, lead to problems. The formation of alkali-chromate and alkali chromium sulphate as well as the presence of chromium VI present environmental problems.
Insofar Al2O3 containing products have been developed produced by the addition of alumina or Magnesium Aluminum Spinel (MgAl2O4) to a brick mixture (MgO-matrix) . These qualities being free of chromium oxide partly present very good mechanical properties but they require mostly expensive and high quality raw materials.
DE 35 27 789 A1 describes ordinary ceramic workpieces within the manufacturing of which during the firing process minerals of the system R+2Oxc3x97R23+O3 are formed, wherein R2+ shall be magnesium and iron and R+3 aluminum, chromium and/or iron respectively. Besides an often unspecific formation of the said minerals during the firing process such bricks are as well not sufficiently alkali resistant or resistant against melts.
DE 44 03 869 C2 describes refractory masses and workpieces formed thereof, comprising, besides MgO sinter a pre-synthesized spinel of the hercynite-type. Such bricks have been proved extremely good especially because of their high micro-structural elasticity, But their resistance against alkali- or alkali salt attack should be better.
It is an object of the invention t o provide a refractory ceramic mass, which, after being processed into burnt workpieces, provides mechanical properties and a ductility comparable with corresponding data of bricks according to DE 44 03 869 C2 and further presenting an improved resistance against alkali- or alkali salt attack. The brick should be usable in furnaces, in which an alkali- or alkali salt resistance especially in combination with a reduced thermal conductivity is required.